Body clock questions, answered
Plain answers to common questions about the circadian rhythm, the body clock that times sleep, alertness and daily activity. Each answer lists the research and health sources it draws on.
- What is an actogram?An actogram charts activity over many days, one row per day. How to read one, why it is double-plotted and what a drifting pattern means.
- How can you find out your circadian rhythm?Use a chronotype questionnaire, a two-week sleep and daylight diary, and step timing from a phone or watch to see your body clock at home.
- Can a smartwatch or phone track your circadian rhythm?Partly. Movement, heart rate and skin temperature follow the body clock, so a week or two of data can estimate its timing, regularity and strength.
- How do you reset your circadian rhythm?Fix your wake time, get morning daylight, dim evening light, eat at regular times and stop caffeine early. The clock shifts about an hour a day.
- How does your circadian rhythm change with age?Babies build a rhythm over their early months, teens drift later until about 20, then the clock moves earlier; in older age the rhythm often weakens.
- What is a chronotype, and can it change?Chronotype is your body clock's preferred sleep timing, from very early to very late. How it is measured, what genes do, and how age and light shift it.
- What is social jet lag?Social jet lag is the gap between your body clock and your work or school hours. How to work it out, what it is linked with and how to reduce it.
- How long does jet lag last, and why is flying east harder?Jet lag usually eases in a few days: the body clock shifts about an hour a day going east and 1.5 hours going west. Why east is harder and how light helps.
- How does shift work affect your body clock?Shift work puts sleep at odds with the body clock, so night workers sleep less and worse. What shift work disorder is and what helps day sleep.
- Why does a regular sleep schedule matter?Regular sleep keeps you in step with your body clock. What UK studies link with irregular sleep, what the Sleep Regularity Index is and how to improve it.
General information, not medical advice. If sleep or tiredness problems affect your daily life, talk to a doctor. Reviewed 6 November 2026 by the Actogram team.